Field of Invention
The present invention relates to a current regulator circuit capable of reducing current ripple and a method of reducing current ripple; particularly, it relates to such current regulator circuit capable of reducing current ripple and method of reducing current ripple which reduce the current ripple of a load current according to a peak-to-average difference or a peak-to-valley difference of the current ripple.
Description of Related Art
FIG. 1 shows a schematic diagram of a light emitting diode (LED) power supply circuit 10, which operates to generate an output voltage Vout and an output current Iout, and provide a light emitting device current ILED to an LED circuit 20, wherein the signal waveform of the output voltage Vout is indicated by the waveform shown in the figure. As shown in FIG. 1, a power conversion circuit 30 receives an AC voltage which is generated by an AC power source 40, and the power conversion circuit 30 rectifies the AC voltage and converts the rectified voltage to the output voltage Vout and generate the output current Iout. An output capacitor Cout is connected to the power conversion circuit 30 to filter the output voltage Vout. A light emitting device current ILED, which is generated according to the output current Iout, is provided to the LED circuit 20.
In general, for better power factor correction (PFC), the power conversion circuit 30 typically includes a PFC circuit (not shown, as well known by those skilled in the art, so details thereof are omitted here), which causes the output current Iout (and therefore the light emitting device current ILED) to carry a current ripple with a frequency which is twice the frequency of the AC voltage. For example, if the AC voltage has a frequency of 50 Hz or 60 Hz, the current ripple of the output current Iout will have a frequency of 100 Hz or 120 Hz. 100 Hz to 120 Hz is in a low frequency range, and a capacitor typically used for the output capacitor Cout does not have a capacitance which is capable of filtering out the current ripple with such a low frequency. Therefore, the light emitting device current ILED flowing through the LED circuit 20 will also have a current ripple with the same frequency, which causes the LED circuit 20 to flicker slightly. Human eyes may not perceive the flicker, but such flicker can degrade the images taken by an image taking device such as a camera or a video recorder.
To deal with the above problem, U.S. Pat. No. 9,107,260 B2 discloses an LED driver circuit for canceling the current ripple, and CN patent application 201410040888 discloses a current regulator control circuit and a control method thereof. The above prior art patent and patent application require obtaining information of an absolute level of a load current and using the absolute level as a basis for further processing (e.g., to be compared with a reference voltage). However, the absolute level of the load current will change depending on different LED circuits because different LEDs have different voltage drops. As such, it is difficult to determine a proper reference voltage to be compared with the absolute level of the load current. Besides, because the above prior art patent and patent application obtain the required information by sensing the source voltage of a power switch, and the source voltage carries a ripple with a low frequency, so the prior art requires a capacitor with a relatively higher capacitance, which leads to a higher manufacturing cost. Furthermore, because the prior art requires sensing the absolute level of the load current and processing the sensed signals, and the accumulated voltage drops of multiple LEDs can be huge, the devices used in the prior art need to withstand relatively higher voltages, which also leads to a higher manufacturing cost.
In view of above, the present invention proposes a current regulator circuit, which reduces the current ripple of a load current according to a peak-to-average difference or a peak-to-valley difference of the current ripple, and a corresponding method of reducing current ripple.